Just downloaded and installed LR 2.6. When I opened the last catalog that I worked on ( I make a separate catalog for each client) I found that I had no history states and that my quick collection from last night was gone. I did back-up the cat. when exiting last night, but have never had to use one so don't know if that will restore all or not. But most importantly, I think it's urgent that you know that this happened.